In recent years, a greenhouse effect resulting from an increase of a carbon dioxide (CO2) concentration is pointed out as a cause of global warming phenomena, and there is an urgent need to device an international countermeasure to protect environment in a global scale. Industrial activities have a large responsibility as a generation source of CO2, and there is a trend to suppress discharge of CO2.
As technologies to suppress the increase of an acid gas concentration starting with CO2, there are a development of energy saving products, a separation and recovery technology of discharged acid gas, technologies to use the acid gas as a resource and to isolate and store the acid gas, a switching to alternate energies such as natural energy, atomic energy, and so on which do not discharge the acid gas, and so on.
As a separation technology of the acid gas studied up to now, there are an absorption process, a suction process, a membrane separation process, a cryogenic process, and so on. Among them, the absorption process is suitable for processing a large amount of gas, and an application for a factory, a power station is considered.
Accordingly, a method in which exhaust gas generated when fossil fuel (coal, coal oil, natural gas, and so on) is burned is brought into contact with a chemical absorbent to remove and recover CO2 in exhaust combustion gas, and further a method storing the recovered CO2 are performed throughout the world in a facility such as a thermal power station using the fossil fuel. Besides, acid gas such as hydrogen sulfide (H2S) in addition to CO2 are removed by using the chemical absorbent is proposed.
In general, alkanolamines represented by monoethanolamine (MEA) have been developed from 1930 years as the chemical absorbent used in the absorption process, and it is still used at present. This method is economical and it is easy to increase the removal device in size.
As existing and widely used alkanolamines, there are monoethanolamine, 2-amino-2-methylpropanolamine, methylaminoethanol, ethylaminoethanol, propylaminoethanol, diethanolamine, methyldiethanolamine, dimethylethanolamine, diethylethanolamine, triethanolamine, dimethylamino-1-methylethanol, and so on.
In particular, primary monoethanolamine and so on are widely used because their reaction rates are fast. However, there are problems in which this compound has corrosiveness, is easy to be deteriorated, and requires high energy for regeneration. On the other hand, tertiary methyldiethanolamine has low corrosiveness, and requires low energy for regeneration, but has a defect that an absorption speed is low. Accordingly, a development of a new absorbent improving these points is required.
In recent years, a study for alkanolamine particularly having structural steric hindrance is vigorously tried as the absorbent of acid gas among amino based compounds. The alkanolamine having the steric hindrance has merits in which selectivity of acid gas is very high, and the energy required for regeneration is small.
The reaction speed of the amine based compound having the steric hindrance depends on a degree of reaction hindrance determined by a steric structure thereof. The reaction speed of the amine based compound having the steric hindrance is lower than the secondary amine, for example, such as methylethanolamine, diethanolamine, but higher than the tertiary amine. Besides, 2-amino-2-methylpropanol, 2-piperidineethanol, and so on are known as the alkanolamine to be compounded in the absorbent.
On the other hand, a method using a cyclic amine as the absorbent as the amine based compound having a structure different from the alkanolamines is also known.